1. Technical Field of the Invention
The present invention relates to fuel injection apparatuses or systems for injecting fuel into cylinders of internal combustion engines. More particularly, the invention relates to a fuel injection apparatus for a diesel engine of a motor vehicle, which has a displacement amplifying chamber formed therein and includes a fuel supplier for promptly filling up the displacement amplifying chamber with low-pressure fuel after start of the engine.
2. Description of the Related Art
An existing fuel injection apparatus, which is incorporated in a common rail fuel injection system for a diesel engine of a motor vehicle, includes a high-pressure passage, a low-pressure passage, an actuator, a first and a second piston, a displacement amplifying chamber, and a fuel injection mechanism.
The high-pressure passage is hydraulically connected to a common rail of the system so as to be filled with high-pressure fuel. The low-pressure passage is configured to be filled with leak fuel from the high-pressure passage under a predetermined pressure. The actuator works to displace the first piston. The displacement amplifying chamber, which communicates with the low-pressure passage, works to amplify and transmit to the second piston a displacement of the first piston by means of the low-pressure fuel therein. The fuel injection mechanism is configured to inject the high-pressure fuel from the high-pressure passage into a cylinder of the engine in response to the displacement of the second piston.
In addition to the fuel injection apparatus, the fuel injection system generally includes a feed pump hydraulically connected to a fuel tank and a high-pressure pump hydraulically connected to the common rail. The feed pump works to pre-pressurize and feed to the high-pressure pump fuel from the fuel tank. The high-pressure pump works to further pressurize the fuel from the feed pump to a high pressure and supply the resultant high-pressure fuel to the common rail.
In such a fuel injection system, when there is contained adequate fuel in the fuel tank, the feed pump will suck in only the fuel from the fuel tank. However, when there is left only an extremely small amount of the fuel in the fuel tank, the feed pump will suck in air along with the fuel from the fuel tank. The sucked in air is then introduced into the high-pressure pump, the common rail, the high-pressure and low-pressure passages, and the displacement amplifying chamber, and exists in those places in the form of fine air bubbles.
During operation of the fuel injection apparatus, the low-pressure passage is always filled with the leak fuel from the high-pressure passage under the predetermined pressure. Accordingly, in the displacement amplifying chamber which communicates with the low-pressure passage, the air bubbles are kept small and the fuel density is kept high. Consequently, the displacement amplifying chamber keeps functioning normally.
However, when the fuel injection system is stopped along with the engine, the low-pressure fuel in the low-pressure passage comes to leak out via a check valve that is hydraulically connected to the low-pressure passage to regulate the fuel pressure therein to the predetermined pressure. Consequently, in the displacement amplifying chamber, the fuel pressure decreases accordingly, so that the fine air bubbles grow into large air bubbles and the fuel density decreases (i.e., the percentage of the air bubbles increases).
Further, when the fuel injection system is restarted along with the engine, a certain time period is required for refilling up both the low-pressure passage and the displacement amplifying chamber with the leak fuel from the high-pressure passage and rebuilding the fuel pressure therein up to the predetermined pressure.
Consequently, during the certain time period, the large air bubbles are compressed within the displacement amplifying chamber, so that the displacement amplifying chamber cannot function normally, and thus the fuel injection mechanism cannot inject the high-pressure fuel into the cylinder of the engine in a timely manner.
To solve such a problem, U.S. Pat. No. 6,899,069 discloses an approach according to which: part of the fuel discharged from a feed pump 13 is supplied to a system region 21 (corresponding to the low-pressure passage) via a diversion conduit 38; and filling of a hydraulic coupler 29 (corresponding to the displacement amplifying chamber) disposed within the system region 21 is carried out via an annular leakage gap that is formed between a bore 25 and a piston 24 inserted in the bore 25.
However, the main function of the feed pump 13 is to feed the fuel discharged therefrom to a high-pressure pump 12; thus, only a minority of the fuel discharged from the feed pump 13 is available for supplying the system region 21 . Consequently, with the limited amount of the fuel, it is difficult to promptly fill up the hydraulic coupler 29 after start of the engine.
On the contrary, if the amount of the fuel supplied to the system region 21 is increased for the purpose of promptly filling up the hydraulic coupler 29, the amount of the fuel fed to the high-pressure pump 12 would be accordingly decreased, so that the high-pressure pump 12 cannot supply adequate high-pressure fuel to the common rail and thus to the high-pressure passage.